The present invention relates to a catheter having a variable length balloon. More particularly, it relates to a balloon catheter having an adjustment device for allowing adjustment of an effective balloon inflation length.
Balloon catheters are widely used in a number of different applications. For example, a balloon catheter is highly useful for effectuating and/or finalizing placement of a stent within the urinary tract, a blood vessel, biliary duct, etc., to name but a few. Additionally, a balloon catheter can be used as part of an angioplasty procedure as an efficient and effective method for treating various types of vascular disease. In particular, angioplasty is widely used for opening a stenosis in a coronary artery, although it is also used for the treatment of a stenosis in other parts of the vascular system and other parts of the body.
In its most basic form, a balloon catheter generally includes a catheter shaft and an inflatable balloon. The catheter shaft defines an inflation lumen which extends to a distal end of the catheter shaft. The balloon, in turn, is attached to the distal end of the catheter shaft such that an interior of the balloon is in fluid communication with the inflation lumen. Balloon inflation is achieved by supplying pressurized fluid to the inflation lumen that in turn inflates the balloon.
Obviously, the above-described balloon catheter can and oftentimes does include a number of additional features. For example, the catheter shaft may include additional structure by which the balloon catheter can be directed to a particular site within the human body via a guidewire. In this regard, a number of different guidewire approaches are available, such as fixed wire, over-the-wire, and single operator exchange catheters. Additionally, the catheter shaft can be provided with other lumens for supplying specific therapeutic substances and/or instruments to the treatment site. Regardless of these additional features, the basic balloon catheter design includes a catheter shaft and a balloon fluidly connected to a distal end of the catheter shaft.
In one application of the above-described balloon catheter, a stent is placed over the balloon and delivered to a treatment site. Once properly in place, the balloon is inflated as previously described, causing the stent to expand and lodge against the walls of the particular duct being treated. This can be done as a follow-up to an angioplasty procedure. Alternatively, following stent placement, it may be necessary to re-expand or tack the stent against the duct walls. Once again, this procedure entails positioning the balloon, in a deflated state, within the stent and then inflating the balloon such that the balloon expands the stent.
With the above-described stent applications, balloon inflation length is highly important. With one accepted approach, the balloon inflation length is selected to be slightly longer than the length of a selected stent so that the entire stent, including its ends, is expanded by the balloon. Alternatively, other recognized methods include choosing a balloon inflation length equal to or slightly smaller than that of the stent. It is believed that this technique achieves adequate stent extension while eliminating the opportunity for undesirable contact between the balloon and the duct wall.
Regardless of the particular stent deployment technique, the standard balloon catheter design requires that a physician have on hand several catheters having different length balloons mounted thereon to accommodate different sized stents. Additionally, it may also require the physician to exchange catheters in the middle of a treatment process so that a catheter of proper balloon length can be utilized. Obviously, these factors can increase the cost of the particular procedure, along with the time required for treatment.
In another application of the above-described balloon catheter, the device is guided through the vascular system to a location near a stenosis. Using fluoroscopy, and assisted by a guidewire, a physician guides the balloon catheter the remaining distance through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid under pressure through the inflation lumen in the catheter to the balloon. Inflation of the balloon causes widening of the lumen of the artery to reestablish acceptable blood flow through the artery.
Vascular occlusions to be treated by a balloon catheter can vary dramatically in size or length. With the variation in length of the occlusion, the area to be treated correspondingly varies in length. It is recognized as desirable to match the inflation length of the balloon as closely as possible to the length of the occlusion to be treated. This prevents expanding the balloon to a length otherwise resulting in pressing against a healthy artery wall. Similar to the drawbacks associated with stent application, the standard balloon catheter design requires, during a treatment, that a physician have on hand several catheters having different length balloons mounted thereon. It may also require the physician to exchange catheters in the middle of the treatment process so that a catheter of proper balloon length can be utilized.
The above problems can be overcome by incorporating a variable length balloon with a single catheter shaft which allows selecting the inflation length of the balloon at the time of or during treatment. Fogarty et al. (U.S. Pat. No. 4,564,014) and Saab (U.S. Pat. No. 5,246,421), the disclosures of which are incorporated herein by reference, disclose catheters incorporating a variable length balloon in a dilation catheter.
Fogarty et al. discloses a catheter including an elongated elastomeric tube closed at its distal end and extending the full length of the catheter. A telescopic sheath is received around the elastomeric tube, which has a distal primary section that is movable relative to the elastomeric tube and a proximal secondary section secured against movement relative to the elastomeric tube. A guidewire is disposed within and extends through the full length of the elastomeric tube with the guidewire having its distal end secured to the distal end of the tube, and its proximal end extending from the proximal end of the tube. The length of the balloon is thus adjusted by moving the distal primary section of the sheath while maintaining the position of the elastomeric tube and proximal secondary section of the sheath.
To facilitate movement of the primary sheath section relative to the elastomeric tube, Fogarty et al. discloses that the elastomeric tube may be stretched lengthwise to reduce its diametrical cross-section by extending the guidewire which is fixed to the distal end of the elastomeric tube. The fixing of the guidewire to the distal end of the elastomeric tube, although aiding in adjusting the size of the balloon, prevents use as an over-the-wire device. Further, the Fogarty et al. device requires that the telescopic sheath extend virtually the entire length of the elastomeric tube, increasing costs and opportunity for sheath movement. In other words, due to its length, the sheath can easily move upon inflation, creating unforeseen problems during use. Along these same lines, because the primary sheath is slidable relative to the secondary sheath, the primary sheath is free to move upon balloon inflation.
Saab also discloses an adjustable-length balloon dilation catheter apparatus incorporating an adjustable sheath which is externally manipulated to partially surround and contain the dilation balloon segment of the catheter while the catheter balloon segments are expanded during a treatment procedure. Saab discloses an adjustable sheath which is substantially co-axial with the catheter and substantially surrounds the catheter body, balloon and catheter tip. Saab discloses that the sheath may run the full length of the catheter or be provided at the distal end of a relatively stiff, controlled catheter, with the latter being co-axially mounted relative to the balloon catheter. Thus, similar to Fogarty et al., the Saab device includes a sheath extending along virtually the entire catheter shaft, thus giving rise to many of the problems described above. Additionally, while Saab briefly mentions that the sheath can be "fixed" by a clamping device or other conventional fastening techniques, no such disclosure or other teaching is provided. Thus, while Saab does provide one version of a variable length balloon catheter, this device provides no assurances that upon inflation, the balloon length will not unexpectedly change.